Experimental infection and transmission ofOrientia Tsutsugamushiin adultLeptotrombidium deliensefollowing inoculation with cultured rickettsiae

Abstract

Strains of Orientia tsutsugamushi (Hayashi) grown in cell culture or chicken egg embryos were inoculated into uninfected Leptotrombidium deliense (Walch) adults to investigate the potential for growth and persistence of rickettsiae in mites. Adult mites were not adversely affected by the injection procedure and O. tsutsugamushi persisted for up to 14 days. Transovarial transmission of O. tsutsugamushi in the progeny of a single adult was observed for three generations. Although only 2 to 20% of larvae from this infected adult fed to repletion on mice, the transstadial transmission rate was 100% in these mites. This is the first time that this method has been used to infect adult mites with O. tsutsugamushi, resulting in transovarial and transstadial transmission.

Variable clinical responses of a scrub typhus outbred mouse model to feeding by Orientia tsutsugamushi infected mites

“…Owing to lack of CD-1 mice in our laboratory, we studied responses by ICR mice. The scrub typhus-mouse model developed helped better understand scrub typhus (Frances et al 2000a(Frances et al , 2001Frances and Linthicum 2002;Lerdthusnee et al 2002;Phasomkusolsil et al 2009) but a complete description of our mouse model and its clinical response following feeding by infected vector mites has not been described previously. Mouse clinical outcomes and virulence of each chigger line are critical for vaccine experimental design which is the ultimate goal for scrub typhus prevention and eradication.…”

“…Several species of laboratory animals have been utilized in the development of a vaccine for scrub typhus, with mice being used most extensively (Ridgway et al 1986). Laboratory mice have been used to characterize the role of chiggers in their transmission of O. tsutsugamushi to vertebrate hosts (Frances 2005;Frances et al 2000aFrances et al , 2001Frances et al , 2002Lerdthusnee et al 2002;Phasomkusolsil et al 2009). But the study of mice clinical presentation of scrub typhus disease following a natural feeding procedure has never been described fully or published elsewhere.…”

Research Progress on Leptotrombidium deliense

“…(2) From the natural population of the suspected chigger mite species, the agent of the disease, O. tsutsugamushi , can be successfully detected or isolated. (3) All the transmission can be done and repeated in the laboratory, including artificial infection, stinging transmission and transovarial transmission [52–54]. The transovarial transmission means that the pathogen, O. tsutsugamushi , can be passed from female chigger mites to their offspring (the next generation) through their egg production.…”

“…Occasionally, the chiggers might sting and suck their hosts for the second time, but it was seldom observed in previous studies [12]. When the first generation of the larvae sucks and obtains the pathogen of scrub typhus ( O. tsutsugamushi ), the pathogen must be transferred to the second generation of the larvae, otherwise, the transmission process will not be completed, and the suspected chigger mite will not be an effective vector [7,12,54]. …”

“…Female mites ( L. deliense ) infected with O. tsutsugamushi also seemed normal relative to uninfected mites, and both the infected and uninfected mites had the same fecundity, namely, the same quantity of egg production [53]. The inoculated adults of L. deliense with O. tsutsugamushi (Hayashi type) showed no abnormal reactions with the persistence of O. tsutsugamushi in the mites for 14 days, and O. tsutsugamushi was passed to the third generation of the mites with 100% of cross-transmission among different generations through the transovarial transmission [54]. …”